EVALUATION OF LACTATIONAL EXCRETION OF UREA AND AMMONIA IN DAIRY CATTLE HERDS

Abstract

The aim of the study was to evaluate the lactational unit production of urea and ammonia emissions from cows kept in eastern Poland. The study covered 1089 lactations of Polish Holstein-Friesian cows born between 1992 and 2018 in 15 cattle herds located in the Mazovia and Podlasie voivodships. The amount of urea excreted in urine and nitrogen compounds in cow feces was calculated based on the following regression equations: (y = 15.46 urea concentration in milk (g/L) + 193.4); y = 11.42 urea concentration in milk (g/L) + 41.93); y = 4.05 urea concentration in milk (g/L) + 151.47). Several factors affecting the total production of urea were examined. Four groups of animals were distinguished according to their milk yield from a 305-day lactation (<6000; 6001-8000; 8001-10000; >10000 kg); three groups based on year of birth (1992-2000; 2001-2010; 2011-2018); four age groups (first lactation; second lactation; third lactation; fourth to twelfth lactation); and three groups according to urea content in milk (1-150; 151-250; >250 mg/L). The results of the study showed that the average concentration of urea in cow urine was 78.6 kg and the ammonia emission from a lactating cow was 44.6 kg. The study demonstrated a large variation in the amount of nitrogen compounds excreted in feces and the degree of ammonia emission risk among animals. The main factors differentiating the amount of nitrogen compounds in urine and feces and the level of ammonia emission into the atmosphere included the cow's production level, year of birth, and urea content in milk.